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Engine RPM fluctuation

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hcourier(at)cox.net
Guest

Posted: Wed May 02, 2007 5:42 am Post subject: Engine RPM fluctuation

Hello,

  

     Have been having a strange and undiagnosed problem with  my right engine.  I fly a 680 FLP with the Mr. RPM conversion to IO-720  engines.  Recently, primarily on takeoff and climb the left ending has been  randomly dropping 50, 100, and sometimes 300-400  RPM numerous times, then  returning to normal takeoff or climb RPM (2,650 Takeoff, 2,500 Climb).   Manifold pressure goes up slightly in such instances. Have seen it happen during  high speed, full power taxi runs, then sometimes it won't happen at all.   

  

     Have had the, prop governors bench tested with  everything shown to be working fine, fuel filter cleaned, new cylinders recently  put on were borescoped and appeared OK.  The manual turbo mechanism was  checked and nothing was out of adjustment or loose.  Currently the magneto  (dual magneto in one unit) was removed.  There was a small amount of oil on  the bottom contacts, and the upper contact had carbon on them.  The magneto  was sent off for inspection and overhaul...it was near recommended overhaul  time.  

  

     Anyone ever seen this happen to them.  We've talked  to prop guys,...the props were recently overhauled.  No one seems to have a  concrete idea as to what's going on.  We are not even sure the oil in the  magneto contact is the problem, but will find out later this week if that's  it.  We thought the problem was solved after a good number of runs on  the runway and one flight of 1.5 hrs with no problems.  The next flight the  same thing happened again.

  

     Anyone have any problems with water getting in a  magneto...none was found in our magneto.

  

     Thanks.  The amount of knowledge on this website is  tremendous.  Folks here have helped me before.  Thanks. 

  

 Ray Mansfield

     

     

    [quote][b]

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floydgm(at)hotmail.com
Guest

Posted: Wed May 02, 2007 6:33 am Post subject: Engine RPM fluctuation

Ray,

Look at the upper deck reference lines they supply turbo boost pressure to 

the fuel inj nozzles. Look for holes in them and the short hoses from them 

to the nozzle shroud. I have seen them get plugged when they are repaired 

and it restricts the airflow to a nozzle.

Also look the "P" leads over vey closely looking for the shield portion to 

be touching the center conductor.



Mike



_________________________________________________________________

Interest Rates NEAR 39yr LOWS!  $430,000 Mortgage for $1,299/mo - Calculate 

new payment

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nico(at)cybersuperstore.c
Guest

Posted: Wed May 02, 2007 9:01 am Post subject: Engine RPM fluctuation

Hi Ray,  

I hope this helps. It’s not rocket science, but just checking a box for you might be worth sharing this. If the manifold pressure goes up when the RPM goes down, isn’t that an indication that the engine is developing power and that something external to the power plant itself is consuming power, such as when one reduces RPM by setting a coarser pitch? Wouldn’t the MP go down and the RPM remain constant (at that power setting) if a fuel blockage occurs?  

Does the RPM variation disappear in cruise?  

Nico  

   

         

  

From: owner-commander-list-server(at)matronics.com [mailto:owner-commander-list-server(at)matronics.com] On Behalf Of Ray Mansfield

 Sent: Wednesday, May 02, 2007 6:41 AM

 To: commander-list(at)matronics.com

 Subject: Engine RPM fluctuation  

  

     

Hello,  

    

   

    

    Have been having a strange and undiagnosed problem with my right engine.  I fly a 680 FLP with the Mr. RPM conversion to IO-720 engines.  Recently, primarily on takeoff and climb the left ending has been randomly dropping 50, 100, and sometimes 300-400  RPM numerous times, then returning to normal takeoff or climb RPM (2,650 Takeoff, 2,500 Climb).  Manifold pressure goes up slightly in such instances. Have seen it happen during high speed, full power taxi runs, then sometimes it won't happen at all.    

    

   

    

    Have had the, prop governors bench tested with everything shown to be working fine, fuel filter cleaned, new cylinders recently put on were borescoped and appeared OK.  The manual turbo mechanism was checked and nothing was out of adjustment or loose.  Currently the magneto (dual magneto in one unit) was removed.  There was a small amount of oil on the bottom contacts, and the upper contact had carbon on them.  The magneto was sent off for inspection and overhaul...it was near recommended overhaul time.    

    

   

    

    Anyone ever seen this happen to them.  We've talked to prop guys,...the props were recently overhauled.  No one seems to have a concrete idea as to what's going on.  We are not even sure the oil in the magneto contact is the problem, but will find out later this week if that's it.  We thought the problem was solved after a good number of runs on the runway and one flight of 1.5 hrs with no problems.  The next flight the same thing happened again.  

    

   

    

    Anyone have any problems with water getting in a magneto...none was found in our magneto.  

    

   

    

    Thanks.  The amount of knowledge on this website is tremendous.  Folks here have helped me before.  Thanks.   

    

   

    

Ray Mansfield  

    

      

    

      

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       [quote][b]

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bobf(at)feldtman.com
Guest

Posted: Wed May 02, 2007 9:40 am Post subject: Engine RPM fluctuation

I had to have my prop governor re-worked last year on the IO 540 in my AC500B. Works fine now. I'd say if you have >1-2% RPM fluctuation you need it fixed, certainly any more than 50RPM change. 300 is way too much. The little centrifugal force thingy that spins around and changes a valve position etc needed reworking - had id done in Dallas. Works fine now. 

  

 qualify that - I am NOT a mechanic. - just a surgeon.

  

 bobf



 

 On 5/2/07, Ray Mansfield <hcourier(at)cox.net (hcourier(at)cox.net)> wrote: [quote]  Hello,

  

     Have been having a strange and undiagnosed problem with my right engine.  I fly a 680 FLP with the Mr. RPM conversion to IO-720 engines.  Recently, primarily on takeoff and climb the left ending has been randomly dropping 50, 100, and sometimes 300-400  RPM numerous times, then returning to normal takeoff or climb RPM (2,650 Takeoff, 2,500 Climb).  Manifold pressure goes up slightly in such instances. Have seen it happen during high speed, full power taxi runs, then sometimes it won't happen at all.   

  

     Have had the, prop governors bench tested with everything shown to be working fine, fuel filter cleaned, new cylinders recently put on were borescoped and appeared OK.  The manual turbo mechanism was checked and nothing was out of adjustment or loose.  Currently the magneto (dual magneto in one unit) was removed.  There was a small amount of oil on the bottom contacts, and the upper contact had carbon on them.  The magneto was sent off for inspection and overhaul...it was near recommended overhaul time.   

  

     Anyone ever seen this happen to them.  We've talked to prop guys,...the props were recently overhauled.  No one seems to have a concrete idea as to what's going on.  We are not even sure the oil in the magneto contact is the problem, but will find out later this week if that's it.  We thought the problem was solved after a good number of runs on the runway and one flight of  1.5 hrs with no problems.  The next flight the same thing happened again.

  

     Anyone have any problems with water getting in a magneto...none was found in our magneto.

  

     Thanks.  The amount of knowledge on this website is tremendous.  Folks here have helped me before.  Thanks. 

  

 Ray Mansfield

     

     

 	  Quote: 	
		  

	


[b]

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n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Wed May 02, 2007 12:54 pm Post subject: Re: Engine RPM fluctuation

I think it is a magneto, plug wire, or plug problem.

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_________________
Milt

nypnx211(at)charter.net
Guest

Posted: Wed May 02, 2007 2:59 pm Post subject: Engine RPM fluctuation

--Question ----Is your engine--Carburetor ed or Fuel Injected ? If you have a carburetor,  the throttle shaft bearings wear out and get loose.  At high power setting as on takeoff, this allows the fuel mixture to go lean and reduced power, just when you need all the power the  engine can produce. What takes place, is the loose bearings allows air to be drawn into the carb Ventura ABOVE the fuel level in the main  nozzle, resulting in the lean mixture.  You can easily check for the loose throttle shaft bearings by moving the throttle arm up and down and checking for any slop  in the shaft. You can do this without dissemble any thing, just reach in there and move the throttle arm up and down and see if you have any loose- nesss.  Hoe this is of some help for your problem.

HAPPY LANDINGS, and KEEP e,m FLYING,     



 arm N395V <n395v(at)hughes.net> wrote:    

 	  Quote: 	
		   

 

 I think it is a magneto, plug wire, or plug problem.

 

 --------

 Milt

 2003 F1 Rocket

 2006 Radial Rocket

 website http://www.excaliburaviation.com

 

 

 

 

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steve2(at)sover.net
Guest

Posted: Thu May 03, 2007 8:37 pm Post subject: Engine RPM fluctuation

Ignition problem would show up well on the EGT if you new what to look 

for....... Look for a jump in EGT on a cylinder with a bad plug or 

compromised ignition.



---

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n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Wed May 16, 2007 5:37 pm Post subject: Re: Engine RPM fluctuation

And have we found the cause yet?

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